Piezoelectric microphone



July 4, 1967 C. A. GoY ETAL PIEZOELECTRIC MICROPHONE 2 Sheets-Sheet l Filed June l5, 1964 MSEY 60) /NVENTORS RBEHTC RA CARL A.

July 4, 1967 c. A. Gov ETAL PIEZOELECTRIC MICROPHONE Filed Jun United States Patent 3,329,776 PIEZOELECTRIC MICROPHONE Carl A. Goy, Stevensville, and Robert C. Ramsey, Niles,

Mich., assignors to Electro-Voice Incorporated, Buchanan, Mich., a corporation of Indiana Filed .lune 15, 1964, Ser. No. 375,214 15 Claims. (Cl. 179-1101) The present invention relates generally to microphones, and in particular to microphones employing piezoelectric generating elements.

Piezoelectric microphones have been known prior to the present invention. Such microphones are described, for example, in Acoustical Engineering by Harry F. Olson, D. Van Nostrand Company, Inc., Princeton, NJ. Such microphones utilize a piezoelectric element, such as a Rochelle salt, barium titanate, or lead zirconium titanate element, on which the acoustical waves are impressed, eithe-r directly or through a diaphragm.

Piezoelectric microphones are generally less expensive than most other types of microphones and produce a relatively large electrical output. It is an object of the present invention to provide a piezoelectric microphone construction which facilitates `assembly and further reduces the cost of such microphones.

It is necessary to connect an electrical cable to the electrodes of the piezoelectric element of a piezoelectric microphone. It is a further object of the present invention to `simplify the electrical lconnections to the piezoelectric element.

The electrical output of a piezoelectric microphone is greatly improved by utilizing a diaphragm to drive the piezoelectric element since the diaphragm provides a better match to the acoustical wave-carrying atmosphere. The diaphragm must, however, be mechanically coupled to the piezoelectric element, and prior to the present invention, drive members have been secured on the piezoelectric element and the diaphragm of such microphones. It is an object of the present invention to provide a microphone utilizing a piezoelectric element driven by a diaphragm in which the element is not mechanically afxed to the diaphragm although mechanically coupled thereto.

These and further objects of the present invention will become readily apparent to those skilled in the lart from `a further consideration of this specification, particularly when viewed in the light of the drawings, in which:

FIGURE l is a front elevational view of a microphone constructed according to the teachings of the present invention;

FIGURE 2 is a sectional view taken along the line 2 2 of FIGURE l;

FIGURE '3 is a sectional view taken along the line 3-3 of FIGURE l;

FIGURE 4 is an elevational view of the back of the microphone casing showing the surface thereof which confronts the front and the piezoelectric element;

FIGURE 5 is an isometric view of the boss for mounting the piezoelectric element of the microphone; and

FIGURE 6 is a front elevational view of the microphone with the front plate of the microphone casing removed.

All of the operative elements of the microphone, that is, the diaphragm, the piezoelectric element, and connections thereto, are mounted on a housing 10 of the microphone. The housing 10 has a front 12 and a back 14. The back 14 of the casing 10 has a back plate 16 which has a -pair of generally parallel edges 18 and 20 located at opposite ends thereof and a pair of symmetrically outwardly curved edges 22 and 24 interconnecting the edges 18y and from a roughly rectangular plate. The back plate 16 also is slightly concave on the inner surface thereof, as is clear from FIGURES 2 and 3.

37,329] 76 Patented July 4, 1967 Fice A longitudinal rib 26 extends centrally of the inner surface of the back plate 16 between the edges 18 and 20 thereof. Also, a plurality of ribs, designed 28, 30, and 32 extend radially through a common point 34 on the axis of the rib 26 from the inner surface of the back plate 16, and these ribs 28, 30, and 32 extend to the perimeter of the back plate 16. A rim 36 extends from the inner surface of the back plate 16 about the perimeter of the back plate 16 and generally normal thereto, and the ribs 26, 28, 36, and 32 interesect the rim 36. A cylindrical wall 38 extends coaxially about the common point 34 except for a gap at the rst rib 26. The back 14 of the casing 10 is constructed of plastic material,

such as Implex-R, a product of Dow Chemical Corporation, and the back plate 16, ribs 26, 28, 30, and 32, rim 36 and wall 38 are an integral structure.

The wall 38 extends from the back plate 16 and is provided with a plurality of slots `40 forming a plurality of spaced posts 42, 44, 46, 48, and 50. Each of the posts has a shoulder 52 confronting the common point 34 on the axis of the rst rib 26, and the shoulders 52 comprise flat surfaces disposed on a common plane generally parallel to the back plate 16.

The back plate 1-6 also carries a boss 54 which extends from the first rib 26 and is spaced from the common point 34. The Iboss 54 is located within the cylindrical Wall 38, and the wall 38 is provided with a gap 55 in the region of the rst rib 26 adjacent to the boss 54. The boss 54 has a wall S6 disposed on the side thereof remote from the common point 34, and the wall 56 has a slot 58 therein. The slot 58 is generally rectangular in shape with its longitudinal axis normal to the back plate 16. The boss 54 also has a portion 60 disposed between the wall 56 and the common point 34 which in eifect forms a saddle. The portion 60 has an incline surface 62 extending to a straight ridge 64. The ridge 64 is parallel to the transversed axes of the rectangular slot 58 and disposed in a plane parallel to the plane of the shoulders 52 of the posts. Further, the ridge 64 is disposed between the ends of the rectangular slot 58. The portion 60 of the boss 54 is provided with shoulders 66 and 68 extending from the ends ofthe ridge 64 and spaced from each other by a distance equal to the transverse axis of the rectangular slot 58 in the wall 56.

A piezoelectric element 70 is mounted on the boss 54. The element 70 is quadrangular in shape and elongated, and has one end disposed within the rectangular slot 58 in the wall 56 and `the other end disposed adjacent to and above the common point 34 in the rst rib 26. Between the two ends, the element 70 abuts the ridge 64. The transverse dimension of the piezoelectric element is slightly greater than the transverse dimension of the slot 58 and the distance between the shoulders 66 and 68, so that an interference tit betwen the end of the element 70 and the wall 56 and an interference t between the shoulders 66 and 68 retain the piezoelectric element 70 in position. The surface of the element 70 remote from the back plate 16 abuts the end of the slot 58 remote from the back plate 16, and the element 70 is thereby positioned generally parallel to the back plate 16.

The piezoelectric element is of conventional construction and utilizes a mass of piezoelectric material, such -as barium titanate, or lead zirconium titanate which is electrically polarized in opposite directions relative to a center electrode. In FIGURE 2, the center electrode is shown as a conductor 72 positioned between two quadrangular slabs 74 and 76 of piezoelectrical material. A thin coating 78 of electrically conducting material is disposed on the exterior surface of the slab 74 and a second coating 80 of electrically conducting material is disposed on the exterior surface of the slab 76 to form electrodes for the element 70. The coatings may be of silver, for example, and are electrically insulated from each other so that a stress applied to the element in a direction normal to the :oated surfaces thereof produces charges of opposite sign an the electrodes 78 and 80.

The interior surface of the back 14 of the casing 18 is :oated with a layer of electrically conducting material such as silver, designated 82, except for the portion of the llrst rib 26 including the boss 54 and extending -from the boss to the rim 36, as indicated in FIGURE 4. This portion of the rst rib 26 is provided 'with a pair of spaced pegs 84 and 86 which extend outwardly between the boss 54 `and the rim 36 of the back 14 of the casing 10. The rib Z6 is also provided with a protrusion 88 between the pegs 84 and 86 terminating in a ilat surface in the plane of the surface of the rib 26 remote from the surface of the back plate 16. The material of the back |14 of the casing is electrically insulating, and an electrically conducting clamp in the form of an elongated strip 90 is mounted on the back plate 16 by means of two apertures 92 and 94 spaced by the same distance as the pegs 84 and 86, and the apertures 92 and 94 are disposed about the pegs 84 and 86 and anchored thereby to the back plate 16. The clamp or strip 90 is provided with a lip 96 at one end thereof which is disposed adjacent to the wall 56 of the boss 54, and the lip 96 extends from the back plate to engage the surface of the piezoelectric element 70 confronting the back plate 16, thereby making electrical contact to the electrically conducting electrode 88 of the piezoelectric element 70 and urging the element 70 into abutment with the end of the slot 58 remote from the back plate 16 of the casing. The clamp 90 is constructed of resilient material to spring bias the end of t-he piezoelectric element into this position.

A ilat ring 98 of electrically conducting material, such as aluminum, is disposed in abutment with the flat surface of the shoulders 52 of the posts 42, 44, 46, 48, and 50. The ring 98 has an outer diameter ygreater than the inner diameter of the wall 36 and is positioned coaxially about the common point 34 by the posts. An electrically conducting diaphragm 106 is disposed on the ring 98, and the diaphragm 100 has a circular perimeter with a diameter equal to the outer diameter of the ring 98.

The diaphragm 100 is constructed of electrically conducting material, such as aluminum, and the diaphragm 100 has a circular ilange 102 at its periphery which abuts the confronting surface of the ring 98. A cone 104 is disposed coaxially within the ilange 102 and coupled thereto by a pair of coaxial circular corrugations 106. The cone 1104 extends toward the common point 34 from the plane of the flange 102 thereof, and the center of the cone is provided with a circular offset 108 which abuts the end of the piezoelectric element '70 remote from the boss 54. Contact between the offset 108 of the cone 104 and the piezoelectric element 70 provides electrical contact between the electrode 78 of the element 70 and the electrically conducting coating 82 on the back 14 of the casing 10, and further provides mechanical coupling between the diaphragm 100 and the piezoelectric element 70. The cone 104 of the diaphragm 100 is rigid, but the corrugations 106 provide a compliant surround which provides a spring loading on the offset 108 against .the piezoelectric element 70 and eliminates the necessity of mechanically ailixing the oilset 108 on the piezoelectric element 70.

A fiat circular baille 110 with the same outer diameter as the diaphragm 100 is positioned in abutment with the flange 102 of the diaphragm within the posts 42, 44, 46, 48, and 50. The baille 110 is provided with a plurality of openings 112 to permit sound to pass therethrough. The baille 110 and openings 112 provide a resistance element for reducing the mechanical resonance of the diaphragm and thereby smoothing the high frequency response of Ithe microphone.

The back plate 16 of the microphone also is provided with a pair of parallel ribs 111 and 113 which extend outwardly therefrom and are covered by the electrically conducting layer 82. A cable 114 enters the casing 10 through an opening 116 formed by recesses in the back 14 and front 12 of the casing 10, and has an inner conductor 117 surrounded by a sleeve 118 of electrically insulating material. The sleeve 118 is in turn surrounded by a layer 120 of electrically conducting mesh, and an -outer protective layer 122 of electrically insulating material surrounds the mesh 120. The coating 122 is removed from a portion of the cable 114 to expose a section of wire mesh, designated 120A, and this portion 120A of wire mesh is snugly disposed between the ribs 111 and 113 to form electrical contact with the layer 82 on the interior surface of the back 14 of the casing 10'. The layer 118 land inner conductor 117 protrudes from the mesh layer 120A, and the inner conductor extends from the layer 118 and is disposed within a protruding strap 124 of the strip clamp 90. In this manner, the inner conductor 117 is electrically connected through the strip clamp to one of the electrodes 80 of the piezoelectric element 70, and the electrically conducting mesh of the cable 114 is connected to the other electrode 78 of the piezoelectric element 70 through the electrically conducting coating 82 on the back 14 of the casing 10, the electrically conducting ring 98, and the electrically conducting diaphragm 100.

Five posts 126, 128, 130, 132, and 134 protrude normally from the back plate 16 of the casing in order to mount the front 12 on the back 14. Each of the posts 126, 128, 130, 132, and 134 is provided with a cylindrical axial channel 136. The posts 126 and 128 are located adjacent to two of the corners of the back plate remote from the two ribs 111 and 113, and two of the posts 132 and 134 are disposed adjacent to the `corners near the ribs 111 and 113. The cable 114 extends from the ribs 111 and 113 about a pin 138 and is provided with a second sharp bend `about the post 134 in order to prevent strain on the cable 114 from effecting junction of the inner conductor 117 `and the strip clamp 90. The post 130 is disposed on the opposite side of the rib 26 from the ribs 111 and 113 adjacent to the cylindrical wall 38.

The front 12 has a front plate 142, and ve pegs 144, 146, 148, 150, and 152 protrude rearwardly therefrom. These pegs `are cylindrical in shape and adapted to be disposed within the channels 136 of the posts 126, 128, 130, 132, and 134 and provide an interference fit therewith. The front 12 of the casing 10 has a rim 154 extending rearwardly from the front plate 142 which mates with the rim 36 of the back 14, yand the front 12 is secured upon the back 14 by wedging the pegs of the front 12 into the channels 136 of the posts of the back 14. The front also has a boss 156 which protrudes rearwardly therefrom in alignment with the ribs 111 `and 113 of the back 14, and the end of the boss 156 remote from the front plate 142 abuts the shielded .portion 120A of the cable 122 to secure and maintain the cable in position between the ribs 111 and 113.

The front 12 has a grill 158 confronting the baille 110, .and hence the diaphragm 100. The grill 158 is formed by a plurality of linear grooves 160 which extend therein from the front of the front plate 142 parallel to the longitudinal axis of the casing 10. The grooves 160 are equally spaced and taper inwardly to a common plane. A second plurality of grooves 162 extend inwardly from the back of the front plate 142, each of the grooves 162 being disposed between two adjacent grooves 160.

Each of the grooves 160 communicates with one of the grooves 162 at the rear of the front plate 142 through a slot 164 so that sound may pass through the grill 158. A layer of cloth 166 is cemented on the back surface of the front plate 142 confronting the grooves 162, and the layer of cloth, t-ogether with the baille 110 perform the necessary loading of the diaphragm 100 to provide `a relatively ilat frequency response at higher frequencies.

The microphone described above is constructed in a manner to facilitate assembly. In order to assemble the microphone, the piezoelectric element 70 is rst mounted on the boss 54 with one end protruding from the slot 58 in the wall 56 and the central portion :anchored on the ridge 64. Thereafter, the strip clamp 90 is positioned on the pegs '84 and 86 and the inner conductor 117 of the cable 114 is slipped into the strap 124. The pegs 84 and 86 are then peened and the strap 124 depressed to engage the inner conductor 116 of the cable 122, ,as illustrated in FIGURE 3.

Next, the ring 98 is positioned on the shoulders S2 of the posts 42, 44, 46, 48, and 50. Thereafter, the diaphragm 100 is placed in position on the ring 98, and the baille 110 is placed in position on the diaphragm 100. The front 12 of the casing 10, with the layer of cloth 166 affixed thereto, is then mounted on the back 14 by forcing the pegs 144, 146, 148, 150, rand 152 into the channels 136 in the posts 128, 126, 130, 132, and 134, respectively. A quantity of cement may be employed to make certain that the posts and pegs remain in engagement.

The microphone will only work elfectively as long ias the outset 108 of the diaphragm 100 remains in contact with the electrode 78 of the piezoelectric element 70. For this reason, the diaphragm 100 is placed under tension relative to the piezoelectric element 70, -but a tension less than Vrequired to permanently distort the diaphragm 100 or break the piezoelectric element 70. Dimensional stability between the diaphragm 100 and the piezo electric element 70 is maintained .as a result of providing the back plate 16 of the casing 10 with a plurality of radial ribs extending outwardly to the cylindrical wall 38 which supports the diaphragm 100, and mounting the piezoelectric element on one of these ribs, namely rib 26. In this manner, the distance from the offset 108 of the diaphragm 100 and the end of the piezoelectric element opposite the wall 56 is maintained within narrow limits even though the microphone be dropped or otherwise abused so that mechanical and electrical contact is maintained between the offset 108 of the diaphragm 100 and the electrode 78 of the piezoelectric element 70.

The force between the oifset 108 of the diaphragm 100 rand the end of the piezoelectric element -must be controlled within relatively narrow limits, and the ring 98 serves as a means for controlling this force. It is dii'licult to `control the distance between the plane of the ange 102 and the surface of the offset 108 which abuts the piezoelectric element 70, and the dimensions of the back 14 of the casing, in order to establish the proper pressure between the offset 108 rand the piezoelectric element 70. The ring 98 may be controlled to far more restricted tolerances than the diaphragm 100 or the back 14 of the casing, `and the thickness of the ring may -thus be selected to provide the proper tension between -the piezoelectric element 70 and the oifset 108 of the cone 100.

Those skilled in the art will readily devise many modications for the microphone herein described, Further, many .applications will become apparent to those skilled in the art for the structures herein set forth. It is therefore intended that the scope of `the present invention be not limited by the foregoing disclosure, but yrather only by the `appended claims.

The invention claimed is:

1. A microphone comprising, in combination: a diaphragm having a central portion of rigid material extending symmetrically about a central axis from an apex to a base, said central portion being rigid to forces exerted along the axis of symmetry, a yieldable resilient ring portion disposed about the base of the cent-ral portion, and a mounting portion extending about the yieldable resilient ring portion; a casing having a rigid back; rigid means for mounting the mounting portion of the diaphragm on the casing with the apex nearest the back and spaced from the back of the casing; a cantilever mounting structure disposed on the back of the casing, said mounting structure having a ridge normal to a pl-ane traversing the axis of symmetry of the diaphragm .and spaced from said `axis of symmetry, said mounting structure having a seat in said plane on the side of the ridge remote from the apex of the central portion; a bender-type elongated piezoelectric element having one portion adjacent to one end mounted on the seat and a second portion adjacent to the other end in mere contactwith the apex of the diaphragm, said element having a third 4portion disposed between the first and second portions in abutment with the ridge, said yieldable resilient ring portion being displaced from its rest position to maintain a pressure contact between the apex of the diaphragm 'and the second portion of the piezoelectric element.

2. A microphone comprising the combination of claim 1 wherein the cantilever mounting structure and casing are an integral unit and the seat of the mounting structure comprises a wall exten-ding from the back of the casing having an opening therein adapted to accommodate one end of the piezoelectric element.

3. A microphone comprising the combination of claim 1 wherein the rigid means for mounting the diaphragm comprises a ring mounted on the casing and disposed in abutment with the mounting portion of the diaphragm adjacent to the yieldable resilient ring portion of the diaphragm.

4. A microphone comprising the combination of claim 1 wherein the -rigid means for mounting the diaphragm comprises a plurality of posts integral with the b-ack of the casing extending therefrom parallel to the axis of symmetry of the diaphragm and disposed at intervals about said axis, each of said posts having a flat shoulder extending toward the axis of symmetry and the shoulders being disposed in a common plane, a ring resting on the shoulders of the posts 'and having a surface opposite the back of the casing abutting the mounting portion of the diaphragm, said ring being adjacent to Ithe yieldable resilient ring portion of the diaphragm, and means for clamping the mounting portion of the diaphragm against the ring including an apertured cover of said casing mounted on the back of the casing.

5. A microphone comprising the combination of claim 4 wherein a sheet of iibrous material having a plurality of openings is disposed between the diaphragm and the cover of the casing, and a layer of cloth is disposed between the sheet and the cover of the casing.

`6. A microphone comprising the combination of claim 1 wherein the yieldable resilient ring portion of the d-iaphragm is integral with the central portion and the mounting portion and comprises a plurality of equally spaced corrugations extending about the central portion of the diaphragm symmetrical with the axis of symmetry, said mounting portion joining the ring portion at a plane on the opposite side of the base of the central portion from the apex thereof and spaced from the base of the central portion.

7. A microphone comprising the combination of claim 6 wherein the central portion of the diaphragm is a cone, and the yieldable resilient portion extends along a truncated cone from the central portion.

8. A microphone comprising, in combination: a diaphragm having a conical central portion of Arigid material, extending symmetrically .about a central yaxis from an apex i to a base, said central portion being rigid to forces excasing comprising a flat ring rigidly mounted on the casing, the flat mounting portion being in abutment with the surface of the ring opposite the back of the casing; a cantilever mounting structure disposed on the back of the casing, said mounting structure having a ridge normal to a plane traversing the axis of symmetry of the diaphragm and spaced from said axis of symmetry, said mounting structure having a seat in sa-id plane on the side of the ridge remote from the apex of the cone; a bendentype elongated piezoelectric element having one portion adjacent to one end mounted on the seat and a second portion adjacent to the other end in mere contact with the apex of the diaphragm, said element having a third portion disposed between the rst and second portions in abutment with the ridge, said yieldable resilient surround being displaced from its rest portion to maintain a pressu-re contact between the apex of the diaphragm and the second portion of the piezoelectric element.

9. A microphone comprising the combination of claim 8 wherein the at ring of the means for mounting the mounting portion of the diaphragm on the c-asing is a separate part, said dat ring having an inner diameter slightly greater than the outer diameter of the yieldable resilient ring portion of the diaphragm, and said means for mounting the diaphragm including a rigid support for said ring extending from the back of the casing and integral therewith, said support defining a flat plane upon which said ring is seated normal to the axis of symmetry of the diaphragm and spaced from the back of the casing.

10. A microphone comprising, in combination: a diaphragm having a central portion of rigid material extending symmetrically about a central axis from an apex to a base, said central portion being rigid to forces exerted along the axis of symmetry, a yieldable resilient ring portion disposed about the base of the central portion, and a mounting portion extending about the yieldable resilient ring; a casing having a rigid back provided with a plurality of linear outwardly extending ribs extending from a common axis generally normal thereto; rigid means for mounting the mounting portion of the diaphragm on the casing with the axis of symmetry of the central portion of the diaphragm coaxial with the common yaxis of the ribs, the central portion and yieldable resilient portion of the diaphragm being spaced from the back of the casing; a cantilever mounting structure integral with one of the ribs on the back of the casing, said mounting structure having a ridge normal to a plane traversing the axis of symmetry of the diaphragm and spaced from said axis of symmetry, said mounting structure having a seat in said plane on the side of the ridge remote from the apex of the diaphragm; a bender-type elongated piezoelectric element having one portion adjacent to one end mounted on the seat and a second portion adjacent to the other end in mere contact with the apex of the diaphragm, said element having a third portion disposed between the first and second portions in abutment with the ridge, said yieldable resilient surround being displaced from its rest position to maintain a pressure cont-act between the apex of the diaphragm and the second portion of the piezoelectric element.

11. A microphone comprising the combination of claim 10 wherein the diaphragm mounting portion is a flat ring and the means for mounting the mounting portion of the diaphragm on the casing comprises a curved wall integral with the casing extending from the back of the casing toward the mounting portion of the diaphragm, said wall extending symmetrically about the common axis of the diaphragm and the portion of said wall remote from the back forming a flat planal seat, a rin-g having an inner surface conforming loosely to the outer edge of the yieldable resilient portion of the diaphragm and having parallel flat surfaces disposed on the seat yand abutting the flat mounting portion of the diaphragm respectively.

12. A microphone comprising the combination of claim 11 wherein the mounting means for the diaphragm includes a plurality of spaced posts extending from the wall, the seat for the ring being formed by a recess on the side of each post confronting the axis of symmetry of the diaphragm.

13. A microphone comprising, in combination: a diaphragm constructed of electrically conducting material havin-g a central portion of rigid material extending symmetrically about a central axis from an apex to a base, said central portion being rigid to forces exerted along the axis of symmetry, a yield-able resilient ring portion dis- -posed about the base of the central portion, and a mounting portion extending about the yieldable resilient ring portion, the central portion, ring portion and mounting portion being an integral unit; a casing of electrically insulating material having a rigid back; rigid means for mounting the mounting portion of the diaphragm on the casing with the apex nearest the back and spaced from the back of the casing; a cantilever mounting structure disposed on the back of the casing, said mounting structure having a ridge normal to a plane traversing the axis of symmetry of the diaphragm and spaced from said axis of symmetry, said mounting structure having a seat in said plane on the side of the ridge remote from the apex of the cone; a bendertype elongated piezoelectric element having a first electrode on one side thereof and a second electrode on the opposite side thereof, said element being'disposed with the first electrode confronting the back of the casing and one portion adjacent to one end mounted on the seat, a second portion of said piezoelectric element being disposed adjacent to the other end and the second electrode thereon loosely abutting the apex of the diaphragm to provide mechanical and electr-ical contact between the element and the diaphragm, said element having a third portion disposed between the first and second portions in abutment with the ridge, said yieldable resilient surround being displaced from its rest portion to maintain a pressure contact between the apex of the diaphragm and the second portion of the piezoelectric element, a two conductor electrical cable, means for electrically connecting one of said conductors to the diaphragm, and means for electrically connecting the other of said conductors to the first electrode of the piezoelectric element.

14. A microphone comprising, in combination: a diaphragm constructed of electrically conducting material having a central portion of rigid material extending symmetrically about a central axis from an apex to a base, said central portion being rigid to forces exerted along the axis of symmetry, a yieldable resilient ring portion disposed about the base of the central portion, and a flat symmetrical mounting portion extending about the yieldable resilient ring portion; a casing constructed of electrically insulating material having a rigid back provided with a plurality of ribs protruding from the back and extending along straight axes from a common point, said casing having a protruding wall symmetrically disposed about said point having portions terminating on a fiat surface spaced from the back of the casing, the mounting portion of the diaphragm being disposed on the portion of the wall of the casing on said flat surface with the apex of the diaphragm nearest the back and spaced from the back of the casing; a cantilever mounting structure integral with the casing disposed on one of the ribs on the back of the casing, said mounting structure having a ridge normal to a plane traversing the axis of symmetry of the diaphragm and spacedfrom said axis of symmetry, said mounting structure having a wall on the side of the ridge remote from the apex of the cone provided with an `opening; a bender-type elonga-ted piezoelectric element having an electrode on each of two parallel surfaces thereof, said element having one portion adjacent to one end disposed in and extending through the opening in the wall and a second portion carrying one of the electrodes adjacent to the other end of the element in mere contact with the apex of the diaphragm, said element having a third portion disposed between the iirst and second portions in abutment with the ridge, said yieldable resilient surround being displaced from its rest position to maintain a pressure contact between the apex of the diaphragm and the second portion of the piezoelectric element, a strip of electrically conducting material mounted on the rib of the casing having the mounting structure for the piezoelectric element on the side thereof opposite the axis of symmetry, one end of said strip abutting the one electrode of the piezoelectric element; -a layer of electrically conducting 1) to the electrically conducting strip and a second conductor connected to the electrically conduct-ing layer on the casing.

15. A microphone comprising the combination of claim 14 wherein the casing is provided with a cover mounted on the back having apertures confronting the diaphragm to permit sound to enter the casing, said cover urging the mounting port-ion of the diaphragm on the at portions of the wall.

No references cited.

KATHLEEN H. CLAFFY, Primary Examiner.

A. MCGILL, Assistant Examiner. 

1. A MICROPHONE COMPRISING, IN COMBINATION: A DIAPHRAGM HAVING A CENTRAL PORTION OF RIGID MATERIAL EXTENDING SYMMETRICALLY ABOUT A CENTRAL AXIS FROM AN APEX TO A BASE, SAID CENTRAL PORTION BEING RIGID TO FORCES EXERTED ALONG THE AXIS OF SYMMETRY, A YIELDABLE RESILIENT RING PORTION DISPOSED ABOUT THE BASE OF THE CENTRAL PORTION, AND A MOUNTING PORTION EXTENDING ABOUT THE YIELDABLE RESILIENT RING PORTION; A CASING HAVING A RIGID BACK; RIGID MEANS FOR MOUNTING THE MOUNTING PORTION OF THE DIAPHRAGM ON THE CASING WITH THE APEX NEAREST THE BACK AND SPACED FROM THE BACK OF THE CASING; A CANTILEVER MOUNTING STRUCTURE DISPOSED ON THE BACK OF THE CASING, SAID MOUNTING STRUCTURE HAVING A RIDGE NORMAL TO A PLANE TRAVERSING THE AXIS OF SYMMETRY OF THE DIAPHRAGM AND SPACED FROM SAID AXIS OF SYMMETRY, SAID MOUNTING STRUCTURE HAVING A SEAT IN SAID PLANE ON THE SIDE OF THE RIDGE REMOTE FROM THE APEX OF THE CENTRAL PORTION; A BENDER-TYPE ELONGATED PIEZOELECTRIC ELEMENT HAVING ONE PORTION ADJACENT TO ONE END MOUNTED ON THE SEAT AND A SECOND PORTION ADJACENT TO THE OTHER END IN MERE CONTACT WITH THE APEX OF THE DIAPHRAGM, SAID ELEMENT HAVING A THIRD PORTION DISPOSED BETWEEN THE FIRST AND SECOND PORTIONS IN ABUTMENT WITH THE RIDGE, SAID YIELDABLE RESILIENT RING PORTION BEING DISPLACED FROM ITS REST POSITION TO MAINTAIN A PRESSURE CONTACT BETWEEN THE APEX OF THE DIAPHRAGM AND THE SECOND PORTION OF THE PIEZOELECTRIC ELEMENT. 